Novel Snake Venom Ligand Dendroaspis Natriuretic Peptide Is Selective for Natriuretic Peptide Receptor-A in Human Heart

Abstract

Abstract-The natriuretic peptides are considered to be cardioprotective; however, their receptors have not been identified in human myocardium using radiolabeled analogs. Dendroaspis natriuretic peptide (DNP) has been recently identified as a new member of this peptide family and is thought to be less susceptible to enzymatic degradation. Therefore, we have developed the novel radiolabeled analog [ 125 I]-DNP and used this to localize high-affinity (K D ϭ0.2 nmol/L), saturable, specific binding sites in adult human heart (nϭ6) and coronary artery (nϭ8). In competition binding experiments, atrial natriuretic peptide and brain type natriuretic peptide had greater affinity for [125 I]-DNP binding sites than C-type natriuretic peptide and the natriuretic peptide receptor (NPR)-C ligand, cANF. This rank order of potency suggested binding of [125 I]-DNP was specific to NPR-A. Messenger RNA encoding NPR-A was identified in left ventricle and coronary artery smooth muscle, and expression was confirmed by immunocytochemical studies at the protein level. In addition, fluorescence dual labeling immunocytochemistry localized NPR-A protein to cardiomyocytes, endocardial endothelial cells, and smooth muscle of intramyocardial vessels. Importantly, we demonstrated a significant downregulation in the density of NPR-A in heart and coronary artery of patients with ischemic heart disease that may explain, in part, the attenuated natriuretic peptide response reported in this patient group. Key Words: Dendroaspis natriuretic peptide Ⅲ heart failure Ⅲ downregulation Ⅲ natriuretic peptide receptor-A T he heart contributes to the regulation of cardiovascular homeostasis by synthesizing and secreting 2 natriuretic peptide hormones: atrial natriuretic peptide (ANP) 1 and brain type natriuretic peptide (BNP). 2 ANP and BNP protect the heart from volume overload by inducing potent natriuresis, diuresis, and vasodilatation. Other cardiac protective roles involve attenuation of cardiac hypertrophy, suppression of both the renin-angiotensin-aldosterone system and sympathetic nervous system activity, while enhancing vagal reflexes. 3 These effects result in decreased preload and after-load to the heart, which further prevents the development of pathologic cardiac hypertrophy and the progression to heart failure (HF).In situations of cardiac stress, the heart responds by increasing the secretion of natriuretic peptides from the ventricles, resulting in significantly enhanced circulating levels of ANP 4 and BNP. 5 The plasma concentration of these peptides, in particular BNP, has been strongly associated with the degree of left ventricular dysfunction and is being used as a diagnostic and prognostic marker for HF. 6,7 Despite the increase in circulating ANP and BNP, the natriuretic, diuretic, and vasodilatory efficacy of these peptides are dramatically reduced in HF. 8,9 This may reflect increased metabolism or clearance of natriuretic peptides from circulation and/or downregulation of functional natriuretic peptide receptors (NPRs), although o...

Natriuretic peptides and therapeutic applications

“…Moreover, in binding experiments (where cultured rat aortic myocytes were exposed to 125 I-ANP in the presence of increasing concentrations of DNP or unlabeled ANP), DNP prevented 125 I-ANP from binding to cultured rat aortic myocytes [5]. More recently, in the human myocardium, Singh et al [11] demonstrated the selectivity of DNP for NPR-A using a radioiodinated analog of DNP. In competition binding experiments, the rank order of potency for NPR-A was DNP > BNP-ANP ) CNP [11].…”

“…More recently, in the human myocardium, Singh et al [11] demonstrated the selectivity of DNP for NPR-A using a radioiodinated analog of DNP. In competition binding experiments, the rank order of potency for NPR-A was DNP > BNP-ANP ) CNP [11]. DNP-like immunoactivity has been detected in isolated arteries and veins from humans [91], in human plasma (with elevated levels in HF patients versus normal subjects) and atrial myocardium [6].…”

“…They bind to natriuretic peptide receptor A (NPR-A) [10], which is widely distributed in the human myocardium [11]. Both NPs are released in response to myocardial wall stretch [9], which is exaggerated in heart failure (HF) where cardiac filling pressures are elevated [12,13].…”

Dendroaspis natriuretic peptide relaxes gastric antral circular smooth muscle of guinea-pig through the cGMP/cGMP-dependent protein kinase pathway

“…DNP is a recently isolated peptide that contains 38 amino residues and shares structural and functional properties with the other members of the natriuretic peptide family [2] . Studies about its physiologic functions mainly focus on cardiovascular [3][4][5] , genital [6] , and urinary systems [7] . Evolutionary studies [8] have suggested the presence of DNP-like immunoreactivity in rat colon, and the DNP-like molecule may control colonic motility as a local regulator.…”

Visualizing the Basis for Paracrine Natriuretic Peptide Signaling in Human Heart

“…14 The authors developed a novel radiolabeled DNP analogue, 125 I-DNP, and used this to localize high affinity ANP-binding sites in the human heart. They complemented these studies with immunocytochemical studies with a commercially available anti-NPR-A antibody.…”